WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
metal (at the end of the electrode) to break up into fine small
particles.
(5) The coatings contain ingredients such as silicates that,
when melted, form a slag over the melted weld and base metal.
Since the slag solidifies at a relatively slow rate, it holds the
heat and allows the underlying metal to cool and solidify slowly.
This slow solidification of the metal precludes the trapping of
gases within the weld and permits solid impurities to float to
the surface.
Slow cooling also has an annealing effect on the
weld deposit.
(6) The physical characteristics of the weld deposit are
modified by incorporating alloying materials in the electrode
coating.
Also, the fluxing action of the slag will produce a
weld of a better quality and permit welding at higher speeds.
(7) The coating insulates the sides of the electrode so that
the arc, at the end of the electrode, is concentrated into a
confined area.
This facilitates welding in a deep "U" or "V"
groove.
(8) The coating produces a cup, cone, or sheath, as shown in
figure 2, view A, on page 7, at the tip of the electrode, which
acts as a shield, concentrates and directs the arc, reduces heat
losses, and increases the temperature at the end of the
electrode.
f.
Polarity of Welding Current (figure 2, view B).
(1) The electrode
polarity recommendations established by the
manufacturer should
be followed when a specific type of electrode
is being used. The
polarity recommended may be either "straight"
or "reverse."
In
straight polarity, the electrode is in the
negative side of
the circuit.
With reverse polarity, the
electrode is in the
positive side of the circuit.
(2) In general, straight polarity is used for all mild-steel,
bare, or lightly coated electrodes.
With electrodes of this
type, the greater heat is developed at the workpiece being welded
which is the positive side of the current. However, when heavy-
coated electrodes are used, the gases given off in the arc may
alter the heat conditions so
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